1. Field of the Invention
The present invention relates to a bidirectional charge pump, and more particularly to a bidirectional charge pump used in CMOS memory devices such as EPROMs, EEPROMs and Flash EPROMs.
2. Discussion of the Related Art
In several integrated circuits it is necessary to generate, internally to the chip, voltages which are higher than or opposite in sign of the supply voltage of the chip. This can be done by means of charge pumps. For example, in a single-power-supply Flash EPROM, it is necessary to generate a positive voltage higher than the supply voltage (VDD) for programming memory cells of the EPROM, and a negative voltage for erasing the memory cells.
Up to now, distinct charge pumps have been used to generate different voltages: positive charge pumps for generating voltages higher than the supply voltage, and negative charge pumps for generating negative voltages.
On the other hand, it is known that the main problem of the integration of a charge pump is the large chip area occupied by the capacitors of the charge pump. The necessity of providing more than one charge pump exacerbates this problem.